The overall objectives of this project are to identify proteins which regulate and/or participate in DNA replication and/or repair using the Novikoff hepatoma as a model system for eukaryotic DNA synthesis. The DNA polymerases have been purified and subsequently used to screen for proteins which stimulate the in vitro reaction. Several factors have been identified and purified to varying degrees. A double-strand specific exonuclease, mammalian DNase V, has been purified to homogeneity and characterized. A novel DNA-binding protein has also been found. Each of these factors is being characterized as individual proteins and then with respect to its interaction with the cellular DNA polymerases. The goal is to establish a role for each action with the cellular DNA polymerases. The goal is to establish a role for each in DNA synthesis in vivo, and to construct multienzymes complexes for DNA replication or repair in vitro.